1. Field of the Invention
The present invention generally relates to earth-boring rotary drill bits, and to methods of manufacturing such earth-boring rotary drill bits. More particularly, the present invention generally relates to earth-boring rotary drill bits that include a bit body substantially formed of a particle-matrix composite material, and to methods of manufacturing such earth-boring drill bits.
2. State of the Art
Rotary drill bits are commonly used for drilling bore holes or wells in earth formations. Rotary drill bits include two primary configurations. One configuration is the roller cone bit, which typically includes three roller cones mounted on support legs that extend from a bit body. Each roller cone is configured to spin or rotate on a support leg. Cutting teeth typically are provided on the outer surfaces of each roller cone for cutting rock and other earth formations. The cutting teeth often are coated with an abrasive hard (“hardfacing”) material. Such materials often include tungsten carbide particles dispersed throughout a metal alloy matrix material. Alternatively, receptacles are provided on the outer surfaces of each roller cone into which hardmetal inserts are secured to form the cutting elements. The roller cone drill bit may be placed in a bore hole such that the roller cones are adjacent the earth formation to be drilled. As the drill bit is rotated, the roller cones roll across the surface of the formation, the cutting teeth crushing the underlying formation.
A second configuration of a rotary drill bit is the fixed-cutter bit (often referred to as a “drag” bit), which typically includes a plurality of cutting elements secured to a face region of a bit body. Generally, the cutting elements of a fixed-cutter type drill bit have either a disk shape or a substantially cylindrical shape. A hard, super-abrasive material, such as mutually bonded particles of polycrystalline diamond, may be provided on a substantially circular end surface of each cutting element to provide a cutting surface. Such cutting elements are often referred to as “polycrystalline diamond compact” (PDC) cutters. Typically, the cutting elements are fabricated separately from the bit body and secured within pockets formed in the outer surface of the bit body. A bonding material such as an adhesive or, more typically, a braze alloy may be used to secure the cutting elements to the bit body. The fixed-cutter drill bit may be placed in a bore hole such that the cutting elements are adjacent the earth formation to be drilled. As the drill bit is rotated, the cutting elements scrape across and shear away the surface of the underlying formation.
The bit body of a rotary drill bit typically is secured to a hardened steel shank having an American Petroleum Institute (API) threaded pin for attaching the drill bit to a drill string. The drill string includes tubular pipe and equipment segments coupled end-to-end between the drill bit and other drilling equipment at the surface. Equipment such as a rotary table or top drive may be used for rotating the drill string and the drill bit within the bore hole. Alternatively, the shank of the drill bit may be coupled directly to the drive shaft of a down-hole motor, which then may be used to rotate the drill bit.
The bit body of a rotary drill bit may be formed from steel. Alternatively, the bit body may be formed from a particle-matrix composite material. Such materials include hard particles randomly dispersed throughout a matrix material (often referred to as a “binder” material). Such bit bodies typically are formed by embedding a steel blank in a carbide particulate material volume, such as particles of tungsten carbide, and infiltrating the particulate carbide material with a matrix material, such as a copper alloy. Drill bits that have a bit body formed from such a particle-matrix composite material may exhibit increased erosion and wear resistance, but lower strength and toughness relative to drill bits having steel bit bodies.
A conventional earth-boring rotary drill bit 10 that has a bit body including a particle-matrix composite material is illustrated in FIG. 1. As seen therein, the drill bit 10 includes a bit body 12 that is secured to a steel shank 20. The bit body 12 includes a crown 14, and a steel blank 16 that is embedded in the crown 14. The crown 14 includes a particle-matrix composite material such as, for example, particles of tungsten carbide embedded in a copper alloy matrix material. The bit body 12 is secured to the steel shank 20 by way of a threaded connection 22 and a weld 24 that extends around the drill bit 10 on an exterior surface thereof along an interface between the bit body 12 and the steel shank 20. The steel shank 20 includes an API threaded pin 28 for attaching the drill bit 10 to a drill string (not shown).
The bit body 12 includes wings or blades 30, which are separated by junk slots 32. Internal fluid passageways 42 extend between the face 18 of the bit body 12 and a longitudinal bore 40, which extends through the steel shank 20 and partially through the bit body 12. Nozzle inserts (not shown) may be provided at face 18 of the bit body 12 within the internal fluid passageways 42.
A plurality of PDC cutters 34 is provided on the face 18 of the bit body 12. The PDC cutters 34 may be provided along the blades 30 within pockets 36 formed in the face 18 of the bit body 12, and may be supported from behind by buttresses 38, which may be integrally formed with the crown 14 of the bit body 12.
The steel blank 16 shown in FIG. 1 is generally cylindrically tubular. Alternatively, the steel blank 16 may have a fairly complex configuration and may include external protrusions corresponding to blades 30 or other features extending on the face 18 of the bit body 12.
During drilling operations, the drill bit 10 is positioned at the bottom of a well bore hole and rotated while drilling fluid is pumped to the face 18 of the bit body 12 through the longitudinal bore 40 and the internal fluid passageways 42. As the PDC cutters 34 shear or scrape away the underlying earth formation, the formation cuttings and detritus are mixed with and suspended within the drilling fluid, which passes through the junk slots 32 and the annular space between the well bore hole and the drill string to the surface of the earth formation.
Conventionally, bit bodies that include a particle-matrix composite material, such as the previously described bit body 12, have been fabricated by infiltrating hard particles with molten matrix material in graphite molds. The cavities of the graphite molds are conventionally machined with a five-axis machine tool. Fine features are then added to the cavity of the graphite mold by hand-held tools. Additional clay work also may be required to obtain the desired configuration of some features of the bit body. Where necessary, preform elements or displacements (which may comprise ceramic components, graphite components, or resin-coated sand compact components) may be positioned within the mold and used to define the internal fluid passageways 42, cutter pockets 36, junk slots 32, and other external topographic features of the bit body 12. The cavity of the graphite mold is filled with hard particulate carbide material (such as tungsten carbide, titanium carbide, tantalum carbide, etc.). The preformed steel blank 16 may then be positioned in the mold at the appropriate location and orientation. The steel blank 16 typically is at least partially submerged in the particulate carbide material within the mold.
The mold then may be vibrated, or the particles otherwise packed, to decrease the amount of space between adjacent particles of the particulate carbide material. A matrix material, such as a copper-based alloy, may be melted, and the particulate carbide material may be infiltrated with the molten matrix material. The mold and bit body 12 are allowed to cool to solidify the matrix material. The steel blank 16 is bonded to the particle-matrix composite material, which forms the crown 14, upon cooling of the bit body 12 and solidification of the matrix material. Once the bit body 12 has cooled, the bit body 12 is removed from the mold and any displacements are removed from the bit body 12. Destruction of the graphite mold typically is required to remove the bit body 12.
As previously described, destruction of the graphite mold typically is required to remove the bit body 12. After the bit body 12 has been removed from the mold, the bit body 12 may be secured to the steel shank 20. As the particle-matrix composite material used to form the crown 14 is relatively hard and not easily machined, the steel blank 16 is used to secure the bit body 12 to the steel shank 20. Threads may be machined on an exposed surface of the steel blank 16 to provide the threaded connection 22 between the bit body 12 and the steel shank 20. The steel shank 20 may be screwed onto the bit body 12, and the weld 24 then may be provided along the interface between the bit body 12 and the steel shank 20.
The PDC cutters 34 may be bonded to the face 18 of the bit body 12 after the bit body 12 has been cast by, for example, brazing, mechanical affixation, or adhesive affixation. Alternatively, the PDC cutters 34 may be provided within the mold and bonded to the face 18 of the bit body 12 during infiltration or furnacing of the bit body 12 if thermally stable synthetic diamonds, or natural diamonds, are employed.
The molds used to cast bit bodies are difficult to machine due to their size, shape, and material composition. Furthermore, manual operations using hand-held tools are often required to form a mold and to form certain features in the bit body after removing the bit body from the mold, which further complicates the reproducibility of bit bodies. These facts, together with the fact that only one bit body can be cast using a single mold, complicate reproduction of multiple bit bodies having consistent dimensions. As a result, there may be variations in cutter placement in or on the face of the bit bodies. Due to these variations, the shape, strength, and ultimately the performance during drilling of each bit body may vary, which makes it difficult to ascertain the life expectancy of a given drill bit. As a result, the drill bits on a drill string are typically replaced more often than is desirable, in order to prevent unexpected drill bit failures, which results in additional costs.
As may be readily appreciated from the foregoing description, the process of fabricating a bit body that includes a particle-matrix composite material is a somewhat costly, complex, multi-step, labor-intensive process requiring separate fabrication of an intermediate product (the mold) before the end product (the bit body) can be cast. Moreover, the blanks, molds, and any preforms employed must be individually designed and fabricated. While bit bodies that include particle-matrix composite materials may offer significant advantages over prior art steel-body bits in terms of abrasion and erosion-resistance, the lower strength and toughness of such bit bodies prohibit their use in certain applications.
Therefore, it would be desirable to provide a method of manufacturing a bit body that includes a particle-matrix composite material that eliminates the need of a mold, and that provides a bit body of higher strength and toughness that can be easily attached to a shank or other component of a drill string.
Furthermore, the known methods for forming a bit body that includes a particle-matrix composite material require that the matrix material be heated to a temperature above the melting point of the matrix material. Certain materials that exhibit good physical properties for a matrix material are not suitable for use because of detrimental interactions between the particles and matrix, which may occur when the particles are infiltrated by the particular molten matrix material. As a result, a limited number of alloys are suitable for use as a matrix material. Therefore, it would be desirable to provide a method of manufacturing suitable for producing a bit body that includes a particle-matrix composite material that does not require infiltration of hard particles with a molten matrix material.
Additionally, when forming a bit body that includes particle-matrix composite material, during the sintering of the particle-matrix composite material forming the bit body, the bit body shrinks, making it difficult to maintain dimensional control of the bit body being formed. It would be desirable to provide a method of manufacturing a bit body that reduces the shrinkage of the bit body during the sintering of the particle-matrix composite material.